Thermal Management Efficiently Cooling Satellite Components in Space

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Efficient thermal management is a key challenge in space exploration. To address this, Fraunhofer HHI is developing laser-based processes that selectively texture metal surfaces, thereby significantly improving heat dissipation.

Space is a vacuum—and this poses a challenge for space-qualified electronics: heat cannot be dissipated to the surrounding environment through conduction, so components can overheat quickly. The only way to release heat in space is by radiating it into space. Researchers at the Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute (HHI), are addressing this issue by functionalizing metal surfaces so that they can radiate heat with very high efficiency in a vacuum.

In this process, heat is converted into thermal radiation via a radiator. For this method to work efficiently, the material used must emit thermal radiation as effectively as possible.The researchers have developed such surface treatments in various projects, including in collaboration with the Fraunhofer Excellence Cluster Advanced Photon Sources (CAPS).

“Since bare metal surfaces—such as aluminum outer walls of satellites, the exterior of rocket nozzles, or enclosures containing power electronics—radiate heat very poorly, we roughen them using lasers. The rough, structured surface effectively acts like a radiator and emits heat very efficiently,” says Prof. Dr. Eike Hübner, head of the research group and scientist at Fraunhofer HHI.

We can functionalize all geometries accordingly—even complex shapes, such as curved surfaces.

Prof. Dr. Eike Hübner

Passive Cooling Based on Laser-Structured Surfaces

The metals are irradiated with a femtosecond laser, causing part of the surface to vaporize. Due to the extremely short laser pulses, the bulk material remains undamaged. Cones are laser-etched into the previously smooth surface, each on the order of one micrometer in size.Using this laser structuring technique, researchers at Fraunhofer HHI have succeeded in increasing the thermal emissivity of roughened surfaces made of aluminum, stainless steel, titanium, or copper to 95 to 99 percent. By comparison, the emissivity of untreated pure metals is only about ten percent.

The advantage of this method is that the surface is physically optimized without chemically altering the material. In addition, structured surfaces enable cost savings during launch, as the launch weight of launch vehicles is reduced by eliminating previously used paint coatings.Unlike painted surfaces, which release solvents over time, this also eliminates the risk of outgassing—the release of gases in space.

In tests, the structured aluminum surfaces withstood temperatures of up to 1,200 degrees Fahrenheit. Since they remain stable up to the respective melting point of the metal used, they are not damaged even at temperatures above 1,200 degrees Fahrenheit when applied to suitable materials.

Optimization of Color and Process

So far, the laser-treated, milled surface appears black. Hübner and his team are currently researching ways to make the functionalized areas appear white.“Depending on which side of the Earth they are on, satellites are exposed to solar radiation. Black surfaces absorb sunlight, causing the radiator to heat up. We want to avoid this issue by using white surfaces that reflect sunlight,” the researcher explains.

In addition, the team further developed the laser process in collaboration with Azimut Space GmbH.The costly and sensitive femtosecond laser techniques are expected to be replaced in the future by more affordable and robust nanosecond laser processes, which, under a reactive gas atmosphere—i.e., pure oxygen—can produce comparable milled structures in metal surfaces.“The process will be somewhat slower, and we will only achieve a thermal emissivity of about 85 percent. However, this will significantly reduce investment costs,” says Hübner.

Material Samples from the ISS on Their Way Back to Earth

Some laser-structured samples made of aluminum and titanium from Fraunhofer HHI have been in space for testing purposes since December 2024.In a project with the European Space Agency (ESA) and with the participation of Azimut Space GmbH, the highly thermally emissive surfaces were installed on the exterior of the International Space Station (ISS), facing the direction of flight, as radiative cooling elements for evaluation under real operating conditions.

The metal samples are now on their way back to Earth. The analysis and examination of material aging, any potential damage, and changes in thermal emissivity are therefore still pending.

Prof. Dr. Eike Hübner

The researchers plan to commercialize their findings together with his colleague Hanan Al-Haddar and his colleague Dr. Ahmad Abdalwareth from Fraunhofer HHI through the start-up Dythalis.The Fraunhofer spin-off is scheduled to launch in May of this year and primarily targets manufacturers of satellites and small propulsion systems as its customer base.One month later, from June 10 to 14, the researchers will present electronic housings and nozzles structured using femtosecond lasers at the ILA 2026 in Berlin (Germany), at the Fraunhofer joint “Space” booth in Hall B 240.